Apparatus for the production of a ray of slow neutrons



Aug. 19, 1941. 2,253,035

HARTMUT ISRAEL KALLMANN, FORMERLY KNOWN AS HARTMUT KALLMANN ETAL.

APPARATUS FOR THE PRODUCTION OF A RAY 0F SLOW NEUTRONS Filed Sept. 15, 1939 Patented Aug. 19, 1941 APPARATUS FOR THE PRODUCTION OF A BAY OF SLOW NEUTRON S Hartmut Israel Kallmann, formerly known as Hartmut Kallmann, and Ernst Kuhn, Berlin, Germany, assignors to I. G. Farbenindustrie Berlin-Charlottenburg,

Aktiengesellschaft,

Frankfort-on-the-Main, Germany, a corporation of Germany Application September 15, 1939, Serial No. 295,156 In Germany September 16, 1938 1 Claim.

As is well known slow neutrons are produced if a hydrogen-containing substance is exposed to a beam of rapid neutrons. The slow neutrons are produced as a result of collisions between the rapid neutrons and the hydrogen nuclei. In general, in apparatus that has been previously proposed, the source of rapid neutrons is situated within the hydrogen-containing substance, in a hollow space that is free from this hydrogencontaining substance, for example in the interior of'a block of paraffin wax or of a water container. The source of rapid neutrons may be a target of beryllium or lithium, subjected to bombardment by ions, for example, deuterons. In such apparatus the concentration of slow neutrons is greatest in the internal hollow space in which the source of rapid neutrons is situated. The concentration of the slow neutrons decreases considerably in the surrounding hydrogen-containing substance in a direction from inside to outside. Outside the hydrogen-containing substance the intensity of the slow neutron with a given strength of the source of rapid neutrons is determined by the extent in the radial direction, from the position of the neutron source, of the vessel receiving the hydrogen-containing substance. In order to obtain a ray of slow neutrons that is as intense as possible outside the apparatus, it is convenient to provide in the hyrogen-containing substance a channel that is free from this substance and which leads from the inside to the outside so that the slow neutrons, the density of which is greatest in the interior, are able to pass unhindered from the inside to the outside. In apparatus of this kind that has already been proposed, rapid neutrons also pass through the channel to a considerable extent, because the channel in this apparatus is always directed to the point at which the source of rapid neutrons is situated. Thus, it is not possible with this apparatus to produce a beam of slow neutrons that contains only a few rapid neutrons. However, rapid and slow neutrons act in quite a difierent manner on radiated substances that are exposed to them. For certain purposes it is important to produce a beam of slow neutrons that is as free as possible from rapid neutrons without at the same time reducing the intensity of the slow neutrons, and this is the object of the present invention.

According to the invention, a channel that is free from the hydrogen-containing substance and which allows the slow neutrons to pass out, is directed not to the point of the apparatus from which the rapid neutrons are emitted, but to som other point of the inner hollow chamber which is free from the hydrogen-containing substance. However, this gives rise to practically no reduction in the intensity of the emergent ray of slow neutrons because the concentration of the slow neutrons in the interior of the hollow chamber is almost constant at least in the neighborhood of the source of the rapid neutrons and because the distribution of the slow neutrons has no preferred direction. If, in accordance with the invention, the channel that is free from hydrogen-containing substance is arranged in some such manner that it is not directed towards the source of rapid neutrons as is illustrated in the accompanying drawing, which is a diagrammatic sectional elevation of one form of apparatus, the slow neutrons are able to pass to the outside just as in the usual manner, but the rapid neutrons are absorbed by the hydrogen-containing substance as before, because before they reach the outside they have to pass through a hydrogencontaining layer of practically the same thickness as if no channel were provided. The principles of the invention are illustrated in the accompanying drawing which is a diagrammatic representation of apparatus embodying the principles of the invention. In the drawing 4 denotes the hydrogen-containing substance, for example, paraflin wax, the inner hollow chamber that is free from the hydrogen-containing substance, 2 the source of rapid neutrons, comprising, for example, a target of beryllium bombarded by a beam of deuterons represented by the arrow and 3 the channel leading the slow neutrons to the outside. As will be apparent from th drawing, channel 3 passes through the body of hydrogencontaining substance with its inner end adjacent but spaced from the source of fast neutrons, and that it is directed toward a point in chamber I not occupied by the source of fast neutrons, so that fast neutrons from said source cannot pass through said channel to the exterior without passing through a substantial portion of the hydrogen-containing substance and being thereby converted to slow neutrons.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

Apparatus for the production of a beam of slow neutrons by the action of rapid neutrons upon a hydrogen-containing substance, comprising a body of hydrogen-containing substance having a hollow chamber therein, a source of rapid neutrons positioned in said chamber, and

a unidirectional rectilinear channel extending through said body of hydrogen-containing substance from the exterior thereof, the inner end of said channel being adjacent to but spaced from said source of rapid neutrons and said channel being directed toward a portion of said chamber not occupied by said source of rapid neutrons.

HARTMUT ISRAEL KALLMANN. Formerly known as Hartmut Kallmann.

ERNST KUHN. 

